Guardian Angel
by ContrarianDragon
Summary: Someone's been watching over Harry Potter.
1. Chapter 1

**Disclaimer: I do not own either Harry Potter or Percy Jackson, nor do I own any affiliated characters or settings.**

Little Whinging was the perfect neighbourhood. The road was clean, its gardens immaculate, and its houses pristine.

Nico hated it.

The Ghost King was not unused to feeling out of place, but here the sentiment was more pronounced than ever. His torn black clothing did not fit in among the well-kept lawns, nor did his dark combat boots match the bright white pavement. Thankfully, the sun beat down heavily that day, and so barely anybody was outside. The streets were empty as he strode down them, full of purpose. He was looking for a specific place: Number 4 Privet Drive.

At first glance, it looked just the same as any of the other large square houses on the street. The window was open to let in air, and inside the news was playing on the television. Nico could just make out one or two people watching it within.

Something shifted in the hydrangeas. Nico narrowed his eyes, trying to see what had caused the disturbance. Still not being able to tell, he shadow-travelled onto the roof. Then, crouching low so that he wouldn't fall, he peered down at the hydrangea bush, and nearly laughed when he saw what was there.

Quietly, he unzipped his backpack and took out the file. He opened it and nodded as his suspicions were confirmed. Lying down behind the hydrangea bush was his charge, Mr Harry James Potter, the Boy Who Lived.

* * *

" _You are nineteen years old now, Nico. It's time for you to embark on your_ own _quest," said Hecate, "and it's time for me to pay back my debt. In the 1990s, a war was raging in my pet magical community. There was nothing that I could do; the Ancient Laws bound me from interfering. So, I called on help from the future. Now the future is the present. Someone must go, lest time become unravelled."_

" _Do you really think that I'm the one for the job?" Nico asked. "The only experience I've had with witches and wizards has been with their ghosts."_

" _That's more than enough. You've already succeeded. If you hadn't, the world wouldn't look like it does today. If good had lost, all the mortals would know about it."_

* * *

Harry Potter was listening to the news. Not that it deserved to be called news, since the current topic was none other than waterskiing budgerigars. Still, it was a relief to hear. No news was good news, and ever since Voldemort had returned, that had become Harry's mantra.

 _No news is good news._

It was hard to believe, however, when even his own friends weren't bringing him news. It was just so _frustrating_. Their messages had been hinting that there was indeed something happening, but neither of them were telling. It wasn't fair.

A loud _crack!_ pierced the quiet. Harry jumped in shock, and banged his head against the bottom of the window sill. Cursing, he stood up. His head was stinging from the blow.

Unfortunately, he wasn't the only person who that noise had Vernon grabbed him tightly by the throat before he could recover. _"Put - it - away! Now! Before - anybody - sees!"_ He was referring to the wand that Harry had drawn instinctively. Harry hastily complied.

"Get - off - me!" Harry gasped, his lungs screaming for air. He struggled to pry his uncle's fingers from his throat, but had little success until the pain caused him to use accidental magic to make Vernon drop him.

Some of the neighbours were coming out to see what the noise had been. Vernon pretended that it had been a car backfiring, though not very well. When the neighbours stuck around to look for themselves, he smiled maniacally until they went away.

"What the devil do you mean by it, boy?" Vernon growled.

"What do I mean by what?" Harry replied coolly. He was distracted by whoever had caused that sound. He was certain that it had been somebody apparating or disapparating, but couldn't see anybody who could be responsible.

"Making a racket like a bloody starting pistol right outside our - "

"That wasn't me," interjected Harry.

Harry and the Dursleys argued for a few minutes more. Eventually, he stormed away, not caring that there would be consequences later.

Releasing a sigh, he turned around to send one last glare at his ignorant relatives. Then, he did a double take. On the roof - where no person should be - sat an older boy. He looked almost like a soldier, except rather than khaki, he wore black leather. Black jacket, black combat boots - exactly the kind of person that the Dursleys would not want to see near their street, never mind on their roof.

 _Death Eater spy_ , was Harry's first thought. He quickly turned around and made as though he'd never noticed anything, resuming his hasty departure. All the while, he felt the boy's eyes boring into the back of his head.

He forced himself to continue walking slowly until he was sure that he was out of sight. Then, he took off in a dead sprint. All the while, thoughts chased around his head, each loudly demanding his attention. _Who was that? Am I being tailed? How long has this been going on?_

Harry stopped after a couple of minutes, gasping and out of breath. He forced himself to get his breathing under control, before attempting the same with his mind. _Think, Harry. What do you know?_ He replayed the afternoon in his mind. Someone had apparated to or from Privet Drive, and then this strange person had appeared on his rooftop. It would be reasonable to assume that it had been the boy, who was obviously magical, that had done this.

Somewhere in the distance, he heard Dudley and his gang farewelling each other. He might've felt angry enough to approach them, but seeing a suspected Death Eater had effectively sapped any reckless feelings he'd been harbouring. Instead, he sighed and turned away. After a moment's deliberation, he ducked down another road to try to get even further away.

He'd been walking for only a few minutes when it happened. It was just him and his lonely thoughts, so at first he didn't notice the feelings of terror that normally preceded the arrival of Dementors. Then the sky went dark, and the warm evening air turned freezing. Harry's blood ran cold. His wand was drawn without a second thought, but barely an instant passed before they were upon him.

Dementors.

One came from each side of the street. Harry's head whipped back and forth between them, his wide eyes taking in their ragged capes and outstretched arms. It felt as though his heart and turned to ice. Belatedly, he realised that he should be casting a Patronus.

It was with desperation that Harry racked his mind for a happy thought. "Expecto Patronum!" he yelled, but the silvery mist that appeared was weak and barely slowed the cloaked monsters. They were getting closer, perhaps only five metres away. He tried to back into one of the front gardens, but tripped on the curb and ended up falling backwards onto his behind.

Without warning, yet another dark shape swooped down from the rooftops. This one, however, clasped within his hands a dark, shiny blade. Harry watched with wide eyes as the boy that he'd seen earlier stabbed the Dementors, plunging his sword quickly through their fabric-garbed frames. Instead of sucking the boy's soul out like Harry would have expected, they exploded in a rain of black powder.

Breathing heavily, Harry stared up at his saviour, who was cleaning the black stuff off his blade. Once he was done, he turned around and the two locked eyes. Harry felt as though the boy's eyes were piercing right through him, but tried not to look too intimidated as he withstood the glare. He held the stare until his eyes watered. When he could stand it no longer, he turned away for a second to blink and wipe the water out of his eyes.

When he turned back, the boy was gone.

Harry sat there, staring at the place where the other boy had been, his eyes wide. He was sure that there had been no sound to indicate apparition, but the boy was gone all the same.

Behind him, he heard footsteps. He turned sharply, his wand raised before him, but was relieved to see that it was just Mrs Figg, one of his elderly neighbours. She was running towards him, looking rather dishevelled. Harry was hurriedly putting his wand away, already rehearsing excuses for what he was doing, when she whacked him on the arm.

"Don't put it away, idiot boy!" she shrieked. "What if there are more of them? Oh, I'm going to _kill_ Mundungus Fletcher!"

Harry stared at her, dumbfounded. Mrs Figg knew about magic? "What?" he asked blankly. "Who's Mundungus Fletcher?"

She scowled. "An absolute moron, that's who! Left to buy some dodgy cauldrons, when I _told_ him he'd be in for it if he went, and _now_ look! _Dementors_!"

Harry's head spun. "Hang on a second! You're a witch?"

"I'm a _Squib_ , as Mundungus knows _full well_ , so how was I supposed to help fend off the Dementors, even if I got here in time? He left you without cover! Oh, I'm going to flay him alive!" The elderly woman was quite worked up. She waved her hands dramatically as she spoke, illustrating how angry she was.

They started walking quickly back to Privet Drive. "Was this Mundungus person following me?" Harry wondered if Mundungus was the person who had saved him from the Dementors. If so, he should probably tell Mrs Figg, who looked like she was about to tear his head off the next time she saw him.

"Yes, yes. Dumbledore's had somebody watching you for a while now. What, you thought he'd let you go off on your own? Dementors, I say! And now you've broken the Statute of Secrecy, too! MUNDUNGUS FLETCHER, I'M GOING TO _MURDER_ YOU!" she yelled at nothing.

A loud _crack_ echoed through the air. In front of them appeared a man who was decidedly not the person who had saved Harry from the Dementors. He stunk of alcohol and smoke. Matted ginger hair framed bloodshot, baggy eyes. "S'up, Figgy?" he slurred, his eyes taking in the strange pair. "What happened to staying undercover?"

"Undercover?!" repeated Mrs Figg. " _Dementors_ is what happened to undercover! On _your_ watch!"

Mundungus stared incomprehensively. "Dementors in Little Whinging?"

* * *

After dealing with the soul-suckers, Nico shadow travelled onto a nearby rooftop. He felt a bit bad about leaving the younger boy there, but orders were orders.

A strange old woman appeared at the scene shortly afterward. He deemed her not a threat and travelled back to the house. Harry arrived a few minutes later, alone and looking fairly distraught. Within moments his bedroom light was turned on and Nico heard a bed heaving under sudden weight.

In the distance, he noticed a dark shape flying toward him. As it got closer, he realised that it was an owl. Tied to its talons was an envelope. Nico shook his head. Wizards were strange folk.

Throughout the next few minutes even more owls arrived with mail. Nico counted six in total, including the first one. Harry himself sent at least three notes. Something big must have been going down, he decided. Was it because the Statute of Secrecy had been broken, or was it something else? Was the Ministry trying to figure out why there had been Dementors in Little Whinging, like he was? He couldn't be certain, because he wasn't quite sure how the magical government worked.

After that, it was quiet. Nico was having a mental debate about whether he should go back to Camp Halfblood for the night. Hecate had provided him with an elixir that made it possible for him to shadow travel through time as well as through space, but it was limited. He shouldn't waste it… Still, he was sorely tempted.

It was cold and uncomfortable on the roof. Eventually, his eyes settled on the bed of hydrangeas where Harry had hidden earlier that day. He heaved a sigh and jumped down, his body automatically tucking into a roll as he made impact with the ground. Out of his back he pulled a blanket, which he spread on the ground beneath him. It would be a long night.

Nico was back on the roof by the crack of dawn. He was surprised to see Harry up and doing chores quite early. It occurred to Nico that Harry was treated badly by the Dursleys. His clothes were overlarge and worn, and he was ordered about like a slave. There was clear tension between him and the other family members. Nico resolved to keep an eye on the situation, but there wasn't much that he could do. His job was to ensure Tom Riddle's downfall, not babysit.

He watched Harry for the next three days, but the situation remained the same. Finally, on the fourth day, Nico noticed something out of the ordinary. The Dursleys were leaving the house to attend some kind of lawn competition. The whole situation seemed a bit too perfect. With the Dursleys out of the house, it was an opportune time for another attack on Harry.

It wasn't too long after the Dursleys left that something happened. Nine people - Nico assumed that they were witches and wizards - turned the corner onto Privet Drive. They got into the house with no trouble. Even though they were inside, they were talking so loudly that Nico could hear their loud exclamations.

Fifteen minutes later, the strange group emerged, this time with the addition of Harry. They took off into the night flying on _broomsticks_ , of all things. They truly were witches. They had some sort of spell on them, so they were camouflaged with the night sky. Nico watched them fly off for as long as he could, before he turned away and opened his bag.

He took out Harry's file, and opened it to the page marked _Possible Locations_. Written on the sheet were these words: _The Headquarters of the Order of the Phoenix may be found at 12 Grimmauld Place, London._ He quickly memorised these words before closing the file and putting it back in his backpack. Then, he disappeared.

He materialised again at Grimmauld Place. For a moment, he couldn't see number twelve, but then he blinked and it was there. With an appraising glance, he listed the advantages and disadvantages of the place. Finally, he shrugged and shadow travelled to a nearby motel. For now, his work was done.

* * *

Harry was lying down in his new bed at Grimmauld Place. He couldn't sleep. It had been a hectic day and, once again, the boy in black was on his mind.

He didn't know how the others had missed him. He was sitting _right there_ on the roof. Still, though they had been flying right over him, the members of the Order had not seen him.

Harry didn't know what to think. The young man had saved his life, but why?

* * *

 **A/N. This is my first story on . What do you think? Should I continue? Please review with your thoughts and ideas :)**


	2. Chapter 2

With Harry safe at Grimmauld place for the time being, Nico was finally able to settle in. He'd considered staying at the village near Hogwarts – Hogsmeade, if he remembered correctly – but something told him that would be far too conspicuous. Instead, he rented a room at a local motel.

He paid for it in cash and provided a blank card when asked for identification. The receptionist, a podgy old man named Angus, had stared at it for a few seconds before nodding as though that were the normal way to proceed. (Nico had improved at manipulating the Mist in the last few years, largely thanks to Hazel.) If anyone checked motel's records, they would find him listed as Mr Damon Walker.

Nico di Angelo became a ghost.

Who would care about a drifter hidden at a motel, or a young boy and his sister hidden in a hotel?

The room was small – the few pieces of furniture it contained barely fit inside. A small, hard bed had been pushed into the corner while the sink, miniature fridge and cabinet sat opposite. There was an adjoining room containing a toilet but nothing to wash himself with. It was a seedy, dirty building, but it suited him just fine. Anything could be considered homely when compared with the Underworld.

Hecate had provided him with several items before sending him on his quest. The first was the time-travelling elixir, which hung from his neck in an hourglass-shaped vial. It was made from crystal glass, with golden trimming around the edges. Strange runes had been etched delicately into the glass. They weren't any language or script that Nico recognised. He knew without having to be told that they were enchanted; the etchings had a magical aura.

The second was a leather-bound case containing several potions, poultices and magical trinkets that the Hecate cabin had gifted him. Each individual item was secured to the inside of the case by a thin leather strap. When folded and zipped shut it was no larger than Daedalus' laptop had been.

The third and final gift was a file containing all the information he might need to complete his quest. Hecate had enchanted it so that no matter which page he turned to, it would show the information that he was looking for. The file seemed to grow or shrink depending on how much information he need. Since there was never a shortage of pages, Nico had begun tearing out the parts that he accessed most. He'd taped a profile of Harry on the wall beside his bed, along with other witches and wizards he associated with. Hermione Granger and Ronald Weasley's profiles had been taped just below Harry's, with the Order of the Phoenix and several known Death Eaters taking up the remaining space.

Nico had turned the far wall into a glossary. Words like 'Death Eater', 'Auror' and 'Horcrux' resided there. Above the kitchen were large, colourful maps. Several of them were moving and some changed by the hour.

It felt like Nico had stepped into an alternate universe – there was so much that he needed to learn before he would be able to make sense of it. How would he know if Harry was in danger when he could barely understand the world around him?

At that moment, he was sitting on the bed, back against the wall. On his lap was the file. It was opened to the 'Ministry of Magic' section, specifically the laws regarding regulation of magic. He frowned as he read. "Prohibited?" he muttered, flipping the page. He clearly remembered Harry casting – or attempting to cast – a spell when he was attacked by the Dementors. What were the consequences for that?

The next page allayed his fear somewhat. The punishment for first offences was almost always just a warning, unless the offender had been using the magic with malicious intent. This was blatant self-defence. Still, he felt uneasy. Did he really know that this was a first offense? For all he knew, Harry was a repeat offender. If all was well, what were all those owls for?

He concentrated on the information that he wanted to withdraw and flipped the page. He groaned when he read its contents: Harry was being put to trial.

August 12th. That was just under a weak away. How in Hades would he find a way to help Harry in time?

* * *

"No, I'd definitely never seen him before," whispered Harry. "I'd remember it if I had."

Harry, Ron and Hermione were sitting in the drawing room at Grimmauld place, miserably cleaning out all the strange and dark objects that had been stowed away there. They were crowded around one of the glass cases, with Sirius, Ginny, Fred and George crowded around another.

"That's really disturbing, Harry," said Hermione. "What do you think he wants?"

Harry shook his head and shrugged. "It seemed like he was just there to keep me safe."

"What if he's like Moody?" asked Ron. "Just keeping you alive so you can do something he wants."

Harry shivered. "I hope not." He reached into the glass case and pulled out a book entitled _Nature's Nobility: A Wizarding Genealogy_. "That's revolting."

Hermione made a face at the book. "Do you reckon you've lost him, Harry? He can't know about Grimmauld Place."

"Maybe…" He didn't think so. There was something hard and soldier-like about the boy. Harry could believe that whatever his mission, he wouldn't stop until it was completed.

Ron seemed to pick up on that. "What if he stalks you to Hogwarts?"

Hermione looked at him as if it were obvious. "We'll tell Dumbledore, of course."

"I don't think Dumbledore wants to talk to me," Harry grumbled, thinking of how the older man had avoided him.

"He's just busy, Harry," said Hermione. "Everyone in the Order is. He wants what's best for you"

He nodded, but remained unconvinced. If it weren't for the strange boy saving him, he could have had his soul sucked out by Dementors. That wasn't what was best for him.

He was startled out of his thoughts by Sirius yelling, "Give it back, you mongrel!" They turned to see him wresting a ring out of Kreacher's grasp. The elderly house elf cringed away from his master, spitting racist curses and throwing dirty looks around the room.

Hermione was on her feet immediately. "Don't be so hard on him, Sirius. He doesn't know what he's doing!"

Ron rolled his eyes. "He knows _exactly_ what he's doing. Give it up, already, Hermione!"

Harry sighed. This was the fifth time that day Kreacher had been caught stealing. He threw the genealogy book into a pile with the other dark objects and then reached back into the glass case. While everybody else was distracted, he withdrew a large locket. It was an ugly thing. Harry wasn't sure that even Mrs Black would want to wear it. Still, there was something about it. Something familiar… Harry tried to open it but found that he couldn't. He looked to see if anyone else could help, but they were all still distracted.

He dropped it into his pocket before he could second guess himself.

That locket reminded Harry of his stalker. Even if he wasn't sure why, he knew to follow his instincts. He hadn't survived this long by ignoring them.

The argument resolved itself not long afterwards.

"Blimey, I'm not sure I can take much more of that!" Ron grumbled as he plopped himself onto the ground near Harry.

Hermione joined the boys on the ground. She looked no less exasperated, but for different reasons. Before the two had a chance to start sniping at each other again, Harry asked, "Do you think the wards around Hogwarts would let someone sneak onto the grounds?"

"Probably," said Hermione. "It depends how they arrived. Why?"

"In case the boy in black tries to follow me there."

Hermione gave Harry a blank look.

"Who?" said Ron. He looked confused, too.

Harry blinked. "But– We were just talking about him!"

Ron and Hermione exchanged a worried look. "Are you feeling alright, Harry?" asked Hermione.

A chill ran down his spine. He remembered the way that no one except him had been able to see the boy. Was it possible that he was the only one who could remember him, too?

"Yes," he said. "I- I'm fine. I think I just need something to drink." With that, he fled from the room.

* * *

 **A/N. Sorry about the short chapter, guys! I needed to get some setup in before next chapter, which will be a big one. Harry's got a hearing before the Wizengamot!**

 **Aloever: Yes, the plot will diverge from the books. Nico's presence changes everything. For example, Harry was so startled by him that he went down a different road and nearly ended up facing the Dementors alone. And now he's pocketed the locket. I'm going for a butterfly effect!**

 **Youya: I'll try to work that in :)**

 **CatatonicVanity: Why not both?**

 **Thanks to everybody! As before, concrit is welcome.**


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